Oxford Cambridge and RSA Examinations

GCSE (9-1)

Combined Science A (Gateway)

Unit J250/09: Chemistry

General Certificate of Secondary Education

Mark Scheme for June 2018

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OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of candidates of all ages and abilities. OCR qualifications include AS/A Levels, Diplomas, GCSEs, Cambridge Nationals, Cambridge Technicals, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. OCR is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support, which keep pace with the changing needs of today’s society. This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by examiners. It does not indicate the details of the discussions which took place at an examiners’ meeting before marking commenced. All examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question papers and the report on the examination. © OCR 2018

J250/09 Mark Scheme June 2018

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Annotations available in RM Assessor

Annotation Meaning

Correct response

Incorrect response

Omission mark

Benefit of doubt given

Contradiction

Rounding error

Error in number of significant figures

Error carried forward

Level 1

Level 2

Level 3

Benefit of doubt not given

Noted but no credit given

Ignore

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Abbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions).

Annotation Meaning

/ alternative and acceptable answers for the same marking point

Separates marking points

DO NOT ALLOW Answers which are not worthy of credit

IGNORE Statements which are irrelevant

ALLOW Answers that can be accepted

( ) Words which are not essential to gain credit

__ Underlined words must be present in answer to score a mark

ECF Error carried forward

AW Alternative wording

ORA Or reverse argument

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The breakdown of Assessment Objectives for GCSE (9-1) in Combined Science A.

Assessment Objective

AO1 Demonstrate knowledge and understanding of scientific ideas and scientific techniques and procedures.

AO1.1 Demonstrate knowledge and understanding of scientific ideas.

AO1.2 Demonstrate knowledge and understanding of scientific techniques and procedures.

AO2 Apply knowledge and understanding of scientific ideas and scientific enquiry, techniques and procedures.

AO2.1 Apply knowledge and understanding of scientific ideas.

AO2.2 Apply knowledge and understanding of scientific enquiry, techniques and procedures.

AO3 Analyse information and ideas to interpret and evaluate, make judgements and draw conclusions and develop and improve experimental procedures.

AO3.1

Analyse information and ideas to interpret and evaluate.

AO3.1a Analyse information and ideas to interpret.

AO3.1b Analyse information and ideas to evaluate.

AO3.2 Analyse information and ideas to make judgements and draw conclusions.

AO3.2a Analyse information and ideas to make judgements.

AO3.2b Analyse information and ideas to draw conclusions.

AO3.3 Analyse information and ideas to develop and improve experimental procedures.

AO3.3a Analyse information and ideas to develop experimental procedures.

AO3.3b Analyse information and ideas to improve experimental procedures.

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For answers to Section A if an answer box is blank ALLOW correct indication of answer e.g. circled or underlined.

Question Answer Marks

AO element

Guidance

SECTION A

1 C 1 1.1

2 B 1 2.1

3 D 1 1.1

4 C 1 1.1

5 C 1 1.1

6 D 1 2.1

7 D 1 1.2

8 B 1 1.1

9 A 1 1.1

10 C 1 2.2

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SECTION B

Question Answer Marks AO

element Guidance

11 (a) Covalent bonds identified in tubes

Idea that bonds are (very) strong / there are many bonds / bonds take lots of energy to break

2 2 x 1.1

DO NOT ALLOW either mark for reference to intermolecular forces or ionic bonding Covalent bonds are strong(er) = 2 Giant covalent structures = 2

(b) (nanotubes contain) delocalised / free electrons (electrons) move

2 2 x 1.1

IGNORE ‘conduct electricity’ as this is in the stem. IGNORE references to moving ions

(c) (i) FIRST CHECK THE ANSWER ON THE ANSWER LINE If answer = 4.9 award 2 marks 7.9÷1.6 = 4.9

2 2 x 2.2

ALLOW 5 / 4.94 /4.938 / 4.9375 Check for incorrect rounding e.g. 4.93 would not score 2 marks

(ii) Any one from: Atoms are packed closer together (in metals) / ORA Carbon nanotubes have hollow spaces / holes ORA RAM of iron much bigger than RAM of C

1 2.1 Assume ‘it’ refers to iron unless qualified. Beware of repeats of stem – ‘iron is more dense than carbon’ ALLOW (iron) layers are closer together

(iii) (Covalent) bonds are stronger (than metallic bonds) / more energy needed to break (covalent) bonds / ORA

1 3.2a DO NOT ALLOW Intermolecular forces references Assume ‘they’ relates to carbon

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Question Answer Marks AO

element Guidance

12 (a) Al2O3 1 2.1 ALLOW O3Al2

DO NOT ALLOW Al2O3

(b) Teacher is wrong / student is right (no mark) Any one from: Formula should be Mg(NO3)2

Idea that charges do not balance as Mg ion is 2+ and NO3 is 1- The ratio of ions is 1:2 (Mg:NO3)

1 3.1b Mark is for explanation – Who is right or wrong can be implied in response. ALLOW MgNO3 would be charged (+)

(c) (i) Al2S3 + 6HCl → 2AlCl3 + 3H2S

1 2.1 ALLOW correct multiples

(ii) (H2S) is a gas

1 2.1 ALLOW ‘g’

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Question Answer Marks AO

element Guidance

13 (a) (i) Labelled arrow (activation energy /A) from 1100 to 1600

1 2.1 ALLOW +/- 1 small square ALLOW label of EA for activation energy

(ii) Labelled arrow (energy change /E) from 1100 to 520

1 2.1 ALLOW +/- 1 small square

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Question Answer Marks AO

element Guidance

13 (b) Bond breaking is endothermic / takes in energy AND bond making is exothermic / gives out energy. More energy is given out (in bond making) than is taken in (in bond breaking)

2 2 x 1.1

ALLOW bond breaking absorbs energy or heat ALLOW bond making releases energy or heat IGNORE references to different numbers of bonds, e.g. more bonds made than broken DO NOT ALLOW references to intermolecular bonds ALLOW exothermic reactions give out energy or heat / temperature rises / reactants have more energy than products if no other mark awarded

(c) FIRST CHECK THE ANSWER ON ANSWER LINE

If answer = - 486 KJ/mol award 3 marks (2 x 436) + 498 = 1370 4 x 464 = 1856 1370 – 1856 = - 486 KJ/mol

3 3 x 2.2

ALLOW (2 x 436) + 498 – (4 x 464) for 2 marks

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Question Answer Marks AO

element Guidance

14 (a) Salt AND water AND carbon dioxide 1 1.1 ALLOW in any order

(b) To measure pH / to tell when the acid is neutralised

1 1.2 ALLOW to see if it is acid or alkaline

(c) 1 x 10-1/ 0.1 (mol/dm3)

1 2.2

(d) (i) 3.7

1 2.2 ALLOW 8.9 to 12.6 – must state both lowest and highest value ALLOW 1.6 if anomaly is missed out of the range / 11.0 to 12.6

(d) (ii) Any two from: Identifies result 6 as anomalous for one or both acids Identifies result 2 as anomalous to a lesser extent for one or both acids Idea that the majority of the results (1,3,4 and 5) are repeatable

2 2 x 3.1b

IGNORE suggested improvements to the method

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Question Answer Marks AO

element Guidance

15* Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. Level 3 (5–6 marks) Correctly analyses the information to choose C for the storage box and explains all relevant properties linked to this polymer. AND Applies knowledge and understanding by relating the relative flexibility of polymer A AND B/C to their structure. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3–4 marks) Correctly analyses the information to choose C for the storage box and explains more than one reason for the choice of polymer based on properties. AND Applies knowledge and understanding by relating the relative flexibility of either polymer A OR B/C to its structure. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. Level 1 (1–2 marks) Correctly analyses the information to choose polymer B or C for the storage box and justifies choice based on property. There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 0 marks No response or no response worthy of credit.

6 2 x2.1

2 x 3.2a

2 x

3.2b

AO2.1 Applies of knowledge and understanding of polymer structure.

A is flexible because it has weak intermolecular forces between polymer chains, so the polymer chains can slide over each other

B and C are rigid because they have strong covalent bonds / crosslinks between the polymer chains which require a large amount of energy to break

AO3.2a / AO3.2b Analyses of information about polymers to make judgements and draw conclusions about which polymer is best for the storage box.

Indicative scientific points may include: Polymer C is used for making storage boxes because:

it has a relatively low density, o so isn’t heavy to lift / lightweight

it is strong, o so will not break easily / can carry heavy loads

it is rigid, o so will not bend / cannot be squashed

Level 1 only

Polymer B could be used for making storage boxes because:

it is rigid.

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Question Answer Marks AO

element Guidance

16 (a) Weak intermolecular forces / weak forces between molecules

Idea that only need a small amount of energy to break these forces

2 2 x2.1 DO NOT ALLOW reference to covalent bonds in incorrect context or references to ions

(b) 2 shared pairs of electrons between carbon and one oxygen atom Rest of structure correct

2 2 x2.1 Inner electrons not required but must be correct if shown. ALLOW all dot, all crosses or mixture of dots and crosses.

(c) Any two from:

Transfer of electrons from metals to non-metals

Metals form positive ions and non-metals form negative ions Electrostatic forces / attraction between oppositely charged ions

2 2 x1.1

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Question Answer Marks AO

element Guidance

17 (a) Any four from: Idea that most particles went straight through without being deflected Most of the atom is empty space Idea that a few particles were (slightly) deflected

The nucleus (deflected the alpha particles because it) is positive

Idea that very few particles were (greatly)

deflected back towards the source Most of the mass is found in the small nucleus.

4 4 x1.2 ALLOW ‘some’ as AW for ‘few’ in this marking point only

(b) Any two from: can evaluate ideas / check results / can compare results can share ideas / have different views so that further evidence can be collected Idea that scientists provide information to other scientists or public or other organisations so they can get recognition for their work

2 2 x1.1

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Question Answer Marks AO

element Guidance

17 (c) Electrons shells / electrons orbit /electrons have definite amounts of energy

1 1.1

18 FIRST CHECK THE ANSWER ON ANSWER LINE If answer = 6.4(g) award 2 marks

3.84 ÷ 96 = 0.04 moles 0.04 x 160 = 6.4g OR 96g (of (NH4)2CO3) makes 160g (of NH4NO3) 3.84g (of (NH4)2CO3) makes 6.4g (of NH4NO3)

2 2 x2.2 ALLOW 3.84/96 x 80 = 3.2 for 1 mark as this is only 1 mistake i.e. not used stoichiometry in equation.

19 Any two advantages from: A and/or C shows number and type of atoms A and/or C shows type of bonds B and/or C shows how the atoms are connected in 3D (tetrahedral) B shows the comparative size of the atoms Any two disadvantages from: A only 2D A and/or C no indication of size of atoms B does not show number and type of atoms B does not show type of bonds

4 2 x 3.1a

2 x

3.1b

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